G. HYDROLOGY AND WATER QUALITY 1. - Amazon S3€¦ · · 2013-06-04G. HYDROLOGY AND WATER QUALITY...

L S A A S S O C I A T E S , I N C . J U N E 2 0 1 3

A P P L E C A M P U S 2 P R O J E C T E I RV . S E T T I N G , I M P A C T S A N D M I T I G A T I O N M E A S U R E S

G . H Y D R O L O G Y A N D W A T E R Q U A L I T Y

P:\COC1101 Apple 2 Campus\PRODUCTS\DEIR\Public\5g-Hydrology.doc (06/03/13) PUBLIC REVIEW DRAFT 303

G. HYDROLOGY AND WATER QUALITY

This section describes the existing hydrology setting for the project site, including runoff, drainage, and water quality characteristics, based on available information provided as part of the project application and published reports, and a site reconnaissance conducted in November 2011. Impacts that could result from the proposed project are evaluated, and mitigation measures to reduce signifi-cant impacts are identified, where appropriate. 1. Setting

The following discussion provides an overview of existing hydrology and water quality conditions on the project site, and the associated regulatory setting. a. Climate. The climate of the Cupertino area is characterized as dry-summer subtropical (often referred to as Mediterranean), with cool, wet winters and relatively warmer dry summers. The approximate annualized average high temperature is 71º Fahrenheit (F); the average low is 49º F. The mean annual rainfall in the vicinity of the project site, for the period between 1893 and 2010, was approximately 14.7 inches, the majority of which occurs from October through April.1 During the period of record, annual rainfall has varied from 6.1 inches (1953) to 32.6 inches (1983), with a one-day high of 4.0 inches of precipitation on January 14, 1911. Analysis of long-term precipitation records indicates that wetter and drier cycles lasting several years are common in the region. Severe, damaging rainstorms occur at a frequency of about once every 3 years.2 b. Watershed. The project site is located in the Calabazas Creek Watershed of the West Valley Watershed planning area. Calabazas Creek, which runs through the southeastern corner of the project site, originates at 2,000 feet above sea level in the foothills of the Santa Cruz Mountains and flows northeasterly to Sunnyvale and ultimately to the Guadalupe Slough. As the principal drainage for the watershed, Calabazas Creek is approximately 13 miles long and drains about 14 square miles. According to the San Francisco Bay Regional Water Quality Control Board (RWQCB) Water Quality Control Plan (Basin Plan), beneficial uses of Calabazas Creek water include agricultural, groundwater recharge, aquatic habitat, wildlife, and recreational uses. 3 c. Groundwater Basin. According to the RWQCB Basin Plan, the project site is located within the Santa Clara Valley groundwater basin and the Santa Clara groundwater sub-basin. The Preliminary Geotechnical Interpretive Report prepared for the project site identified groundwater at depths of 59 to 68 feet below the ground surface (bgs).4 Depths to groundwater may vary due to seasonal precipitation and infiltration rates.

1 Western Regional Climate Center, 2011. General Climate Summary, San Jose, CA. Website: www.wrcc.dri.edu/

summary/Climsmcca.html (accessed November 11, 2011). 2 Brown, William M. III, 1988. Historical Setting of the Storm: Perspectives on Population, Development, and

Damaging Rainstorms in the San Francisco Bay Region, in Landslides, Floods, and Marine Effects of the Storm of January 3-5, 1982, in the San Francisco Bay Region, California, Stephen D. Ellen and Gerald F. Wieczorek, Eds., U.S. Geological Survey Professional Paper 1434.

3 San Francisco Bay Regional Water Quality Control Board, 1995. Water Quality Control Plan. Website: www.waterboards.ca.gov/sanfranciscobay/basin_planning.shtml. Appended through 2010.

4 Arup, 2013. Apple Campus 2 Geotechnical Interpretative Report. Issue 3. April 30.





According to the Basin Plan, beneficial uses of the Santa Clara groundwater sub-basin include municipal and domestic, industrial process, industrial service, and agricultural water supply.5 Based on groundwater quality data collected in 2010 by the Santa Clara Valley Water District (SCVWD) and various local water suppliers, groundwater within the Santa Clara sub-basin is of good quality, and generally meets drinking water thresholds (i.e., it does not exceed maximum contaminant level thresholds).6 d. Stormwater Runoff and Drainage. The project site currently contains buildings, parking lots, and other impervious surfaces, and stormwater runoff discharges into drain inlets that convey the runoff via the City storm drainage system into Calabazas Creek, and ultimately into San Francisco Bay. Approximately 133 acres (75 percent) of the project site is currently covered by impervious surfaces. The City storm drainage system was designed to accommodate a 10-year storm event, although the City estimates the system could accommodate a 10-year to 40-year flood with minor overflow along the street gutters, but no flooding in buildings.7 All new development must include improvements to the City’s storm drainage system, if necessary, to create sufficient capacity to accommodate the 10-year storm event.8 e. Flooding, Dam Inundation, and Coastal Hazards. Calabazas Creek has a history of flooding, having experienced major flood events in the vicinity of the project site in 1955, 1980, 1983, 1998, and 2002.9 It is estimated that a major flooding event on Calabazas Creek would result in an average of $11 million (2008 dollars) in damages.10 The $3.5 million Calabazas Creek Improvement Project was designed to address flooding issues along a 4.5-mile segment of Calabazas Creek from Guadalupe Slough to Miller Avenue. The project, which was completed in 2011, included the replacement of a Union Pacific Railroad bridge in Saratoga, erosion repairs at ten locations, creation of a flood detention area south of Saratoga-Sunnyvale Road, and the replacement of the culvert underneath Saratoga-Sunnyvale Road. The improvements were designed to provide 1-percent flood protection (e.g., protect against flooding during the 100-year flood event) along the creek between San Francisco Bay and Miller Avenue, obtain a Letter of Map Revision (LOMR) from the Federal Emergency Management Agency (FEMA) memorializing that protection, and stabilize the channel between Lawrence Expressway and Miller Avenue. Preparation of the LOMR is currently underway. Once the LOMR is obtained, the Calabazas Creek Improvement Project will remove 2,250 parcels in Santa Clara, San Jose, and Cupertino from the existing 100-year floodplain, including the portions of the project site adjacent to Calabazas Creek.11 Figure V.G-1 shows the current flood map for the project site.

5 San Francisco Bay Regional Water Quality Control Board, 1995, op. cit. 6 Santa Clara Valley Water District, 2011. Groundwater Monitoring and Analysis Unit. 2010 Groundwater Quality

Report. June. 7 Cupertino, City of, 2005. City of Cupertino General Plan, 2000-2020. November 15. 8 Santa Clara, County of, 2007. Drainage Manual. August 14. 9 Santa Clara Valley Water District, 2010. Calabazas Creek Flood Protection Project Brochure. Website:

www.valleywater.org/CalabazasCreekFloodProtectionProject.aspx (accessed November 11, 2011). 10 Ibid. 11 Ibid.

CalabazasCreek

CalabazasCreek

CITY OF CUPERTINO060339

CITY OF CUPERTINO060339

ZONE AZONE A

HANCOCK DRHANCOCK DR

ZONE AEZONE AE

1% ANNUAL CHANCEFLOOD DISCHARGE

CONTAINED IN CHANNEL



RID

GE

VIE

WC

T

RID

GE

VIE

WC

T

CITY OF SAN JOSECITY OF SAN JOSE

NOTE: MAP AREA SHOWN ON THIS PANEL ISLOCATED WITHIN TOWNSHIP 7 SOUTH, RANGE2WEST, AND THE QUITO LAND GRANT

NOTE: MAP AREA SHOWN ON THIS PANEL ISLOCATED WITHIN TOWNSHIP 7 SOUTH, RANGE2WEST, AND THE QUITO LAND GRANT

BridgeBridge

SANTA CLARA COUNTYSANTA CLARA COUNTY

QUITO LAND GRANTQUITO LAND GRANT

NT

AN

TA

UA

VE

NT

AN

TA

UA

VE

ZONE XZONE X

MELODY LNMELODY LN

LORNE WAYLORNE WAY

CIT

YO

FC

UP

ER

TIN

OC

ITY

OF

CU

PE

RT

INO





HO

WA

RD

DR

HO

WA

RD

DR

PRUNERIDGE AVEPRUNERIDGE AVE

SW

AL

LO

WD

RS

WA

LL

OW

DR

MILLER AVEMILLER AVE

E HOMESTEAD RDE HOMESTEAD RD

CALABAZAS CREEKCALABAZAS CREEK

FORGER DRFORGER DR

VICKSBURGCT

VICKSBURGCT

ROSEMARIE PLROSEMARIE PL

LEOLA CTLEOLA CT

GIA

NN

INI D

R

GIA

NN

INI D

R

EE

ST

AT

ES

DR

EE

ST

AT

ES

DR

ZONE XZONE X





DA

WS

ON

DR

DA

WS

ON

DR

ME

AD

OW

AV

EM

EA

DO

WA

VE

ZONE DZONE D

VIC

KS

BU

RG

DR

VIC

KS

BU

RG

DR

CITY OFSANTA CLARA

060350

CITY OFSANTA CLARA

060350


CONTAINED IN CULVERT



HU

BB

AR

DA

VE

HU

BB

AR

DA

VE





SULLIVAN DR

SULLIVAN DR

ZONE XZONE X

CalabazasCreek

CalabazasCreek

REVISEDAREA

REVISEDAREA





VALLCO PKWYVALLCO PKWY

SHASTA DRSHASTA DR

ZONE AZONE A

STEVENS CREEK BLVDSTEVENS CREEK BLVD

ZONE AZONE A

NW

OL

FE

RD

NW

OL

FE

RD

SANTA CLARA COUNTYUNINCORPORATED AREAS

060337

SANTA CLARA COUNTYUNINCORPORATED AREAS

060337

RICHWOOD CTRICHWOOD CT

CITY OF SANTA CLARACITY OF SANTA CLARA

ZONE XZONE X

CITY OF SUNNYVALE060352

CITY OF SUNNYVALE060352

ZONE XZONE X





CI T

YO

FS

AN

TA

CL

AR

AC

I TY

OF

SA

NT

AC

LA

RA

FIN

CH

AV

EF

INC

HA

VE

GREENWOOD DRGREENWOOD DR

ZONE AZONE A

CITY OFSAN JOSE

060349

CITY OFSAN JOSE

060349

CITY OF CUPERTINOCITY OF CUPERTINOCITY OF SUNNYVALECITY OF SUNNYVALE

T

JOIN

SP

AN

EL

02

28

Federal Emergency Management Agency

Notice to User: The shown below should beused when placing map orders; the shownabove should be used on insurance applications for the subjectcommunity.

Map NumberCommunity Number

CONTAINS:

COMMUNITY NUMBER PANEL SUFFIX

(SEE MAP INDEX FOR FIRM PANEL LAYOUT)

SANTA CLARA COUNTY,

CALIFORNIA

SANTA CLARA COUNTY 060337 0209 HCUPERTINO, CITY OF 060339 0209 H

SAN JOSE, CITY OF 060349 0209 H

SANTA CLARA, CITY OF 060350 0209 HSUNNYVALE, CITY OF 060352 0209 H

AND INCORPORATED AREAS

Project Site Boundary

(100-Year) Floodplain1% annual chance

0.2% annual chance(500-Year) Floodplain

feet

10000 500

Apple Campus 2 Project EIRFlood ZoneSOURCE: NATIONAL FLOOD INSURANCE PROGRAM, MAY 2009.

I:\COC1101 Apple Campus 2\figures\Fig_VG1.ai (4/25/13)

FIGURE V.G-1





This page intentionally left blank.





Although a large portion of the City of Cupertino could be inundated by failure of the Stevens Creek Dam, located approximately 3.75 miles southwest of the project site, the project site is not located in the dam failure inundation area.12 The City General Plan notes that Stevens Creek Dam meets appli-cable dam safety standards and the probability of its failure is minimal.13 The location of the project site, over 8 miles south of San Francisco Bay, and the elevation of the site (approximately 145 to 175 feet above mean sea level) eliminates the potential for coastal hazards, such as sea level rise, seiche, tsunami, or extreme high tides. f. Water Quality. The quality of surface water and groundwater in the vicinity of the project site is affected by past and current land uses at and near the site. Water quality within the watershed is also affected by the composition of local geologic materials. Water quality in surface and groundwa-ter bodies is regulated by the State Water Resources Control Board and Regional Water Quality Control Boards. The project site is under the jurisdiction of the San Francisco Bay RWQCB, which is responsible for implementation of State and federal water quality protection statutes, regulations, and policies in the vicinity of the project site. The RWQCB implements the Basin Plan, a master policy document for managing water quality in the region. The Basin Plan establishes beneficial water uses for waterways and water bodies within the region. The United States Environmental Protection Agency has designated the entire length of Calabazas Creek as impaired for diazinon, a pesticide commonly used from the 1970s through early 1980s for indoor pest control and gardening uses.14 On November 16, 2005, the RWQCB adopted Resolution No. R2-2005-0063 amending the Basin Plan to establish a program to control diazinon and pesticide-related toxicity in Bay Area urban creeks, including Calabazas Creek.

(1) Municipal Stormwater Management Requirements. Pursuant to Section 402 of the Clean Water Act (CWA) and the Porter-Cologne Water Quality Control Act, municipal stormwater discharges in the City of Cupertino and other member agencies of the Santa Clara Valley Urban Runoff Pollution Prevention Program (SCVURPPP) are regulated under the San Francisco Bay Region Municipal Regional Stormwater National Pollutant Discharge Elimination System (NPDES) Permit, Order No. R2-2009-0074, NPDES Permit No. CAS612008, adopted October 14, 2009 (MRP). MRP Provision C.3 addresses post-construction stormwater management requirements for new development and redevelopment projects that add and/or replace 5,000 square feet or more of impervious area. Provision C.3 requires the City to require incorporation of site design, source control, and stormwater treatment measures into development projects, to minimize the discharge of pollutants in stormwater runoff and non-stormwater discharge, and to prevent increases in runoff

12 Association of Bay Area Governments, 2003. Dam Inundation Hazard Map for Cupertino. Website:

www.abag.ca.gov/bayarea/eqmaps/damfailure/dfpickc.html (accessed November 11, 2011). 13 Cupertino, City of, 2005, op. cit. 14 U.S. Environmental Protection Agency, 2002. 2002 Waterbody Report for Calabazas Creek. Website:

oaspub.epa.gov/tmdl/attains_waterbody.control?p_list_id=CAR206%2E401CALABAZAS%20CREEK&p_cycle=&p_report_type=T.





flows. The MRP requires that Low Impact Development (LID)15 methods be the mechanism for implementing such controls. MRP Provision C.3 requires that stormwater treatment best management practices (BMPs) be designed per the following hydraulic sizing criteria:

Volume Hydraulic Design Basis: Treatment systems whose primary mode of action depends on volume capacity shall be designed to treat stormwater runoff equal to: (a) The maximized stormwater capture volume for the area, on the basis of historical rainfall records, determined using the formula and volume capture coefficients set forth in Urban Runoff Quality Management, Water Environment Federation Manual of Practice No. 23/American Society of Civil Engineers Manual of Practice No. 87, (1998), pages 175-178 (e.g., approximately the 85th percentile 24-hour storm runoff event); or (b) The volume of annual runoff required to achieve 80 percent or more capture, determined in accordance with the methodology set forth in Section 5 of the California Stormwater Quality Associa-tion (CASQA)’s Stormwater Best Management Practice Handbook, New Development and Redevelopment (2003), using local rainfall data;

Flow Hydraulic Design Basis: Treatment systems whose primary mode of action depends on flow capacity shall be sized to treat: (a) 10 percent of the 50-year peak flow rate; (b) the flow of runoff produced by a rain event equal to at least two times the 85th percentile hourly rainfall intensity for the applicable area, based on historical records of hourly rainfall depths; or (c) the flow of runoff resulting from a rain event equal to an intensity of at least 0.2 inches per hour; and

Combination Flow and Volume Design Basis: Treatment systems that use a combination of flow and volume capacity shall be sized to treat at least 80 percent of the total runoff over the life of the project, using local rainfall data.

Effective December 1, 2011, projects must treat 100 percent of the required runoff (based on the selected calculation described above) with LID treatment measures that include harvesting and reuse, infiltration, evapotranspiration, or biotreatment (biotreatment may only be used if the other options are infeasible). Biotreatment areas shall be designed to have a long-term infiltration rate of 5 to 10 inches per hour. In response to Provision C.3, project sponsors are required to submit a Storm Water Management Plan with building plans, to be reviewed and approved by the City of Cupertino Public Works Depart-ment, Environmental Programs Division. The Storm Water Management Plan must be prepared under the direction of a licensed and qualified professional.

(2) Construction General Permit. Pursuant to CWA Section 402 and the Porter-Cologne Water Quality Control Act, on September 2, 2009, the State Board adopted an NPDES General Permit for Storm Water Discharges Associated with Construction and Land Disturbance Activities, Order No. 2009-0009-DWQ, NPDES No. CAS000002 (Construction General Permit). To obtain coverage under the Construction General Permit, the project applicant must provide, via electronic submittal, a Notice of Intent, a Storm Water Pollution Prevention Plan (SWPPP), and other docu-

15 The goal of LID is to reduce runoff and mimic a site’s predevelopment hydrology by minimizing disturbed areas and impervious cover and then infiltrating, storing, detaining, evapotranspiring (i.e., evaporating water from soil and plants), and/or biotreating stormwater runoff close to its source.





ments required by Attachment B of the Construction General Permit. Activities subject to the Construction General Permit include clearing, grading, and disturbances to the ground, such as grubbing or excavation. The permit also covers linear underground and overhead projects such as utility or pipeline installations. Construction activities covered under the Construction General Permit are regulated at a local level by the RWQCB. The Construction General Permit exercises a risk-based permitting approach, and mandates certain requirements based on the risk level of the project (Level 1, Level 2, or Level 3). The risk level of the project is based on the risk of sediment discharge and the receiving water risk. The sediment dis-charge risk depends on the project location and timing (i.e., wet season versus dry season activities). The receiving water risk depends on whether the project would discharge to a sediment-sensitive receiving water, defined by specific beneficial uses of the receiving water in the Basin Plan (e.g., fish migration), a listing on the CWA 303(d) list due to sediment impairment, or having a Total Maximum Daily Load in place to address excessive sedimentation. The risk level determination would be made by the preparer of the SWPPP, which must be prepared prior to construction of the project. The performance standard in the Construction General Permit is that dischargers minimize or prevent pollutants in stormwater discharges and authorized non-stormwater discharges through the use of controls, structures, and management practices that achieve Best Available Technology (BAT) standards for treatment of toxic and non-conventional pollutants and Best Conventional Technology (BCT) standards for treatment of conventional pollutants.16 The permit also imposes numeric action levels (for Level 2 and Level 3 projects) and numeric effluent limits (for Level 3 projects) for pH and turbidity, as well as minimum BMPs that must be implemented at all sites. A SWPPP must be prepared by a Qualified SWPPP Developer that meets the certification require-ments in the Construction General Permit. The purpose of the SWPPP is to: (1) to help identify the sources of sediment and other pollutants that could affect the quality of stormwater discharges; and (2) describe and ensure the implementation of BMPs to reduce or eliminate sediment and other pollutants in stormwater as well as non-stormwater discharges resulting from construction activity. BMPs must be overseen by a Qualified SWPPP Practitioner that meets the requirements outlined in the permit. For Level 2 and Level 3 projects, the discharger must also prepare a Rain Event Action Plan as part of the SWPPP that is designed to protect all exposed portions of the construction site within 48 hours prior to any likely precipitation event. The SWPPP must also include a construction site monitoring program. The monitoring program includes, depending on the project risk level, visual observations of site discharges, water quality monitoring of site discharges (pH, turbidity, and non-visible pollutants, if applicable), and receiving water monitoring (pH, turbidity, suspended sediment concentration, and bioassessment). g. Recycled Water Systems. Recycled water is treated household/commercial wastewater that is used for non-potable irrigation, agricultural, and industrial land uses. The California Department of Health Services establishes water quality and treatment standards for water recycling in Title 22,

16 As defined by U.S. EPA, Best Available Technology (BAT) is a technology-based standard established by the

CWA as the most appropriate means available on a national basis for controlling the direct discharge of toxic and non-conventional pollutants to navigable waters. The BAT effluent limitations guidelines, in general, represent the best existing performance of treatment technologies that are economically achievable. Best Conventional Technology (BCT) is a technology-based standard that applies to treatment of conventional pollutants, such as total suspended solids.





Division 4, Chapter 3 of the California Code of Regulations. Different standards apply to the recycled water depending on whether the water may come into contact with the general public. Apple is currently discussing the potential recycled water line with several agencies, including South Bay Water Recycling, the Santa Clara Valley Water District, City of San Jose, CalWater, and the cities of Sunnyvale, and Santa Clara. Current discussions could include one of several water line routes. At this time, the specific route for the potential recycled water line extension remains uncertain (although the route that would extend the recycled water line from the existing City of Sunnyvale Water Pollution Control Plant along Wolfe Road is the most likely). Please refer to Chapter III, Project Description, for more detail. h. Local Policies. The following section summarizes local policies and regulations that are applicable to hydrology and water quality.

(1) City of Cupertino General Plan. The following policies from the Health and Safety Element of the City of Cupertino General Plan are relevant to the proposed project: Policy 6-46: New Construction in Flood Plains

Adopt stringent land use, zoning and building code regulations limiting new construction in the already urbanized flood hazard areas recognized by the Federal Flood Insurance Administration. Policy 6-47: Dwellings in Natural Flood Plain

Regulate closely all types of habitable development in natural flood plains. This includes prohibiting fill materials and obstructions that may increase flood potential downstream or modify the natural riparian corridors.

(2) City Municipal Code. The City Storm Water Pollution Prevention and Watershed Protection Ordinance (Chapter 9.18) prohibits discharge of anything other than stormwater to a storm drain and requires immediate notification of the Director of Public Works in the event of any accidental discharge. Countermeasures to prevent further occurrences must be implemented before the next precipitation event and documented within 5 days of an accidental discharge. The City Water Resource Protection Ordinance (Chapter 9.19) requires a Streamside Modification Permit for projects adjacent to streams. Issuance of the Streamside Modification Permit is evaluated based on consistency guidelines and standards for land use on properties adjacent to streams. City Municipal Code Chapter 16.52 includes provisions regulating construction in designated flood hazard areas that are designed to prevent damage from flooding. 2. Impacts and Mitigation Measures

This section analyzes the impacts related to hydrology and water quality that could result from imple-mentation of the project. The section begins with criteria of significance, which establish the thresh-olds for determining whether a project impact is significant. The latter part of this section presents the less-than-significant and potentially significant hydrology and water quality impacts associated with the proposed project. Mitigation measures are provided as appropriate.





a. Significance Criteria. The project would have a significant effect on hydrology or water quality if it would:

Violate any water quality standards or waste discharge requirements;

Create or contribute a substantial amount of runoff that would be an additional source of water quality degradation;

Result in substantial erosion or sedimentation on- or off-site that would affect the quality of receiving water;

Create or contribute runoff that would exceed the capacity of existing or planned storm-water drainage systems and/or increase upstream or downstream flooding and require or result in the construction of new stormwater drainage facilities or expansion of existing facilities, the construction of which could cause significant environmental effects;

Place housing within a 100-year flood hazard area as mapped on a federal Flood Hazard Boundary or Flood Insurance Rate Map or other flood hazard delineation map;

Place within a 100-year flood hazard area structures which would impede or redirect flood flows;

Expose people or structures to a substantial risk of loss, injury, or death involving flooding, including flooding as a result of the failure of a levee or dam;

Expose people or structures to a substantial risk of inundation by seiche, tsunami, extreme high tides, and/or sea level rise;

Substantially deplete groundwater supplies or interfere substantially with groundwater recharge such that there would be a significant net deficit in aquifer volume or a lowering of the local groundwater table level;

Substantially alter the existing drainage pattern of the site or area, including through the alteration of the course of a stream or river, in a manner which would result in substantial erosion or siltation on- or off-site;

Substantially alter the existing drainage pattern of the site or area, including through the alteration of the course of a stream or river, or substantially increase the rate or amount of surface runoff in a manner which would result in flooding on- or off-site; or

Otherwise substantially degrade water quality. b. Less-Than-Significant Impacts. This section describes the less-than-significant impacts of the project on hydrology and water quality.

(1) Violate Water Quality Standards During Construction. There may be a potential for stormwater runoff generated during construction of the project to contain contaminants that could affect Calabazas Creek and downstream water bodies and violate water quality standards. However, as discussed below, existing regulatory programs would reduce any potential impacts to a less-than-significant level. Development of the project would require approximately 1,690,000 cubic yards of excavation (net) and 1,620,000 cubic yards of fill (net) for Phase 1 and Phase 2 combined. Phase 1 would result in a balanced site and Phase 2 would require approximately 150,000 cubic yards of soil to be exported





from the site. Phase 1 would require approximately 45,000 cubic yards of top soil import and Phase 2 would require an import of 5,000 cubic yards, for a total top soil import of 50,000 cubic yards. In areas of active construction, soil erosion may result in discharges of sediment-laden stormwater runoff into Calabazas Creek, if not properly controlled (although, with the exception of the provision of fencing, maintenance access, and landscape/tree planting, no building/roadway construction would occur within the 50-foot buffer around Calabazas Creek). Sediment can also be a carrier for other pollutants, such as heavy metals, nutrients, pathogens, oil and grease, fuels, and other petroleum products. In addition to sediment, other pollutants associated with the various phases of construction, such as trash, paint, solvents, sanitary waste from portable restrooms, and concrete curing compounds, can discharge into and impair receiving waters if released during construction. Consistent with the requirements of the Statewide Construction General Permit, the project applicant would be required to prepare and implement a SWPPP designed to reduce potential adverse impacts to surface water quality through the project construction period. The SWPPP must be designed to address the following objectives: (1) all pollutants and their sources, including sources of sediment associated with construction, construction site erosion, and all other activities associated with con-struction activity are controlled; (2) where not otherwise required under a RWQCB permit, all non-stormwater discharges are identified and either eliminated, controlled, or treated; (3) site BMPs are effective and result in the reduction or elimination of pollutants in storm water discharges and authorized non-stormwater discharges from construction activity to the BAT/BCT standard; and (4) stabilization BMPs installed to reduce or eliminate pollutants after construction are completed . The SWPPP must be prepared by a Qualified SWPPP Developer and include the minimum BMPs required in Attachment C of the Construction General Permit for Risk Level 1 dischargers, Attach-ment D for Risk Level 2 dischargers, or Attachment E for Risk Level 3 dischargers (as applicable, based on final determination of the project’s Risk Level status [to be determined as part of the Notice of Intent for coverage under the Construction General Permit]). Based on California Stormwater Quality Association (CASQA) and City guidance, the following are representative of BMPs that the applicant may choose from when preparing the SWPPP and may be required for each phase of the project construction period. In addition, the SWPPP would be prepared in accordance with all applicable provisions of the City Municipal Code, including those pertaining to the containment of litter. Erosion Control BMPs

Scheduling. To reduce the potential for erosion and sediment discharge, construction shall be scheduled to minimize ground disturbance during the rainy season. The project applicant shall:

○ Sequence construction activities to minimize the amount of time that soils remain disturbed.

○ Stabilize all disturbed soils as soon as possible following the completion of ground-disturbing work. As described in more detail below, BMPs for soil stabilization may include preservation of existing vegetation; hydroseeding; use of soil binders; use of hydraulic, wood, or straw mulch, geotextiles and mats; and/or creation of earth dikes and drainage swales. All stabilization measures shall be implemented in accordance with Section 3 of the CASQA Stormwater Best Management Handbook – Construction.





○ Install erosion and sediment control BMPs prior to the start of any ground-disturbing activities.

Preservation of Existing Vegetation. Where feasible, existing vegetation shall be preserved to provide erosion control.

Stabilize Soils. Hydroseeding, geotextile fabrics and mats, mulch, or soil binders shall be used, as appropriate, to reduce erosion on exposed soil surfaces.

Stabilize Streambanks. When working along stream banks or within channels, BMPs shall be implemented to minimize channel erosion and sedimentation. Correctly installed and maintained erosion and sediment controls, such as silt fences, mulch, geotextiles, and hydroseeding, shall be used. To the extent possible, existing vegetation that stabilizes the stream banks shall be preserved.

Earth Dikes, Drainage Swales and Slope Drains. Earth dikes, drainage swales, or slope drains shall be constructed to divert runoff away from exposed soils and stabilized areas, and redirect the runoff to a desired location, such as a sediment basin.

Outlet Protection and Velocity Dissipation Devices. Rock, concrete rubble, or grouted riprap shall be installed at culvert and pipe outlets to drainage conveyances, to prevent scour of the soil caused by concentrated high-velocity flows.

Sediment Control BMPs

Silt Fence/Fiber Roll. Silt fences or fiber rolls shall be installed, checked daily, and effectively maintained around the perimeter of the areas affected by construction, at the toe of slopes, around storm drain inlets, and at outfall areas, to prevent offsite sedimentation.

Street Sweeping and Vacuuming. Areas with visible sediment tracking shall be swept or vacuumed daily with a regenerative air or vacuum-type sweeper not more than 5 years old, to prevent the discharge of sediment into the stormwater drainage system or creeks.

Storm Drain Inlet Protection. Storm drains shall be protected using a filter fabric fence, gravel bag barrier, or other methods, to allow sediments to be filtered or settle out before runoff enters drain inlets.

Check Dams. Barriers shall be constructed of rock, gravel bags, sand bags, or fiber rolls across a constructed swale or drainage ditch, to reduce the effective slope of the channel and the velocity of runoff.

Sediment Traps. Sediment traps shall be constructed where sediment-laden runoff may enter the stormwater drainage systems or creeks. Sediment traps are appropriate for drainage areas less than 5 acres.

Sediment Basins. If used on-site, sediment basins shall be designed according to the method provided in the CASQA Stormwater BMP Handbook – Construction.17 Sediment basins are appropriate for drainage areas of 5 acres or greater.

17 California Stormwater Quality Association, 2003, op. cit.





Wind Erosion Control BMPs

Dust Control. Potable water shall be applied using water trucks to alleviate nuisance caused by dust. Water application rates shall be minimized to prevent erosion and runoff.

Stockpile Management. Silt fences shall be used around the perimeter of stockpiles, and stockpiles shall be covered to prevent wind dispersal of sediment.

Tracking Controls

Stabilized Construction Entrance/Exit. Construction site entrances and exits shall be graded and stabilized to reduce the tracking of mud and dirt onto public roads by construction vehicles. The design and layout of these construction access areas shall be in accordance with the guidance in section TC-1 of the CASQA Stormwater Best Management Handbook Construction.

Stabilized Construction Roadway. Access roads, parking areas, and other on-site vehicle transportation routes shall be stabilized immediately after grading is completed, and frequently maintained to prevent erosion and to control dust.

Tire Wash. A tire washing facility shall be installed at stabilized construction access points to allow for tire washing when vehicles exit the site to prevent tracking of dirt and mud onto public roads. If possible, potable water discharged from fire sprinkler or fire hydrant testing captured on the project site or elsewhere shall be used.

Non-Stormwater Controls

Dewatering. If groundwater dewatering is anticipated, the SWPPP shall include a dewater-ing plan for non-contaminated groundwater that specifies methods of water collection, transport, treatment, and discharge. The discharger shall consult with the RWQCB regard-ing any required permit (other than the Construction General Permit) or Basin Plan condi-tions prior to initial dewatering and discharge to land, storm drains, or receiving waters. Water produced by dewatering shall be impounded in holding tanks, sediment basins, or other holding facilities to settle the solids and provide other treatment as necessary prior to discharge to receiving waters. Discharges of water produced by dewatering shall be controlled to prevent erosion.

Illicit Connection/Discharge Detection and Reporting. Contractors shall regularly inspect the site for evidence of illicit connections, illegal dumping, or potential discharges. Any illicit activities shall be immediately reported to the City.

Vehicle and Equipment Cleaning. Construction equipment shall be washed as needed in a designated stabilized area on-site, or off-site. Steam cleaning shall not be performed on-site. Soap shall be used only if necessary. If soap is deemed necessary, only phosphate-free, biodegradable soaps shall be used for on-site activities. Wash water from on-site activities shall be contained and infiltrated, to avoid discharges to drain inlets and creeks.

Vehicle and Equipment Fueling and Maintenance. Vehicles and equipment shall be inspected daily for leaks. Vehicle maintenance and fueling shall be performed off-site whenever possible. If maintenance and fueling must take place onsite, designated areas shall be located at least 50 feet away from storm drain inlets, drainage courses, and receiv-ing waters. Fueling areas shall be protected with berms and dikes to prevent infiltration, runoff, and to contain spills. Fueling shall be performed on a level grade. Nozzles shall be





equipped with automatic shutoffs to control drips. Stored fuel shall be enclosed or covered. Drip pans shall be used for all vehicle and equipment maintenance activities. Spill kits shall be available in maintenance and fueling areas, and spills shall be removed with absorbent materials and not washed down with water. If spills or leaks occur, contaminated soil and cleanup materials shall be properly disposed.

Paving and Grinding Operations. Proper practices shall be implemented to prevent run-on and runoff, and to properly dispose of waste. Paving and grinding activities shall be avoided during the rainy season, when feasible.

Waste Management and Materials Pollution Control BMPs

Material Delivery, Storage, and Use. Materials such as detergents, concrete compounds, petroleum products and hazardous materials shall be stored in a designated area away from vehicular traffic, drain inlets, and Calabazas Creek. The materials shall be stored on pallets with secondary containment. Spill clean-up materials, material safety data sheets, a material inventory, and emergency contact numbers shall be maintained in the storage area.

Spill Prevention and Control. Proper procedures shall be implemented to contain and clean-up spills and prevent material discharges into the storm drain system.

Waste Management. Solid waste shall be collected in designated areas, and stored in water-tight containers located in a covered area or with secondary containment. No waste shall be left on the site that is not in an enclosed container. Waste shall be removed from the site regularly. Hazardous wastes shall be stored and disposed in accordance with applicable regulatory requirements.

Sanitary/Septic Waste Management. Portable toilets shall be located at least 50 feet away from drain inlets and Calabazas Creek, and out of the flow line to drain inlets and the creek, and away from paved areas.

Stockpile Management. Stockpiles shall be surrounded by sediment controls, covered, and located at least 50 feet from concentrated flows of stormwater, inlets, and Calabazas Creek.

Concrete Waste Management. Concrete washout shall be performed offsite, or in a designated area at least 50 feet away from storm drain inlets or Calabazas Creek. A temporary pit or bermed area shall be constructed where the waste can be discharged and allowed to solidify for proper disposal.

Training. Construction site personnel shall receive training on implementing all BMPs included in the SWPPP, including those related to the containment of loose litter.

With implementation of these BMPs, to be identified in the SWPPP, as required by State law, the project’s stormwater runoff from construction activities would result in a less-than-significant impact on Calabazas Creek.





(2) Violate Water Quality Standards During Project Operation. By consolidating and clustering buildings and making use of underground parking and parking garages, the project design would increase pervious surfaces on the site from 43 acres to 102 acres. In addition, the permeable landscape would be largely contiguous, unlike the current landscaping, which is organized into small areas separated by buildings and parking lots. In general, both of these components of project development would result in a beneficial impact to stormwater runoff quantity and quality, restoring the site’s hydrology to a more natural condition. However, the proposed project includes new access roadways, some surface parking, and landscaping, which are potential sources of various stormwater pollutants, such as sediments, metals, pesticides, petroleum hydrocarbons, nutrients, and trash and debris. Such pollutants may also be present in non-stormwater discharges, such as runoff from irrigation and maintenance activities. If these potential sources of pollutants were not properly controlled, discharges into receiving waters could adversely affect water quality and beneficial uses. However, as outlined below, existing regulatory programs would reduce any potential impacts to a less-than-significant level. In accordance with the Municipal Regional Permit, the project applicant will be required to prepare and implement a Storm Water Management Plan to control pollutants in post-construction stormwater runoff and non-stormwater discharges, which must be submitted for review with the building permit application to the City of Cupertino. The Storm Water Management Plan must be prepared under the direction of a licensed professional registered in California. At a minimum, the Storm Water Management Plan is required to include the following elements:

An inventory of existing natural hydrologic features and significant natural resources.

A description of the existing and proposed site drainage network and connections to drainage off-site.

A division of the site into separate drainage areas, and an inventory of the current and proposed impervious surfaces in each area.

A description of the treatment option for each drainage area (e.g., self-retaining, self-treating, or treatment/flow facility).

Preliminary design, including calculations, for infiltration, treatment, or flow-control facilities, demonstrating their adequacy.

An inventory of potential contaminant sources and strategies for the protection of stormwater quality, to the maximum extent practicable.

A draft Operations and Maintenance plan, including a description of maintenance require-ments, personnel assigned to that maintenance, and the establishment of a means for which the Operations and Maintenance Plan will be funded and implemented in perpetuity.

In accordance with RWQCB and City guidance, the Storm Water Management Plan would also document the incorporation of Low Impact Development (LID) elements into the project design. These LID elements, which have already been incorporated into the project (see Chapter III, Project Description) would include the following strategies:





Preserving Important Hydrologic Features and Functions

Use buffers for filtration, infiltration, and bank stability.

Minimize development on highly permeable soils. Development Siting and Layout

Fit the design to existing drainage patterns to maximize benefits of the existing terrain.

Cluster development to maximize contiguous open space. Using Natural Drainage Systems

Disconnect impervious areas from the storm drainage system and use vegetation, soil amendments, and deep tiling to increase infiltration.

Work to reduce and minimize grading where reasonable and feasible.

Use swales and other landscaping to reduce runoff velocity. The proposed project would incorporate these concepts, including minimizing surface parking lots and other impervious areas (increasing pervious surface coverage from approximately 43 acres to 102 acres), consolidating and clustering buildings, maximizing contiguous open space, disconnecting impervious areas from the storm drainage system, and using swales and other landscaping to reduce runoff velocity. Therefore, implementation of the Storm Water Management Plan, including LID elements, as required under the Municipal Regional Permit, would ensure that stormwater runoff from the project site would not violate water quality standards during project operation.

(3) Result in Flooding. Based on information from the project application, the project would reduce impervious coverage on the site from approximately 75 percent of the site to approximately 41 percent of the site. This reduction in impervious surfaces would tend to increase infiltration of storm-water and reduce flood risks in the vicinity of the site. In accordance with established City require-ments, the project would be required to modify any affected or adjacent drainage infrastructure and stormwater conveyances as necessary to accommodate the 10-year storm. Requirements for modified drainage infrastructure would eliminate any localized flooding that could be caused by the specific location and configuration of proposed impervious surfaces. Therefore, the project would not be expected to result in downstream flooding or require an extensive modification to stormwater infrastructure that would itself result in significant environmental effects. Localized flooding effects could occur due to inadequate storm drainage infrastructure along North Wolfe Road; this potential impact is addressed as Impact HYD-1, below.

(4) 100-Year Flood Zone and Flood Risks. Although part of the southeastern corner of the project site, adjacent to Calabazas Creek, is located in a 100-year flood zone, no structures are proposed within that area. In addition, this area will be removed from the designated 100-year flood zone with obtainment of a LOMR from FEMA, as discussed above. The project site is not within a dam failure inundation area. The distance of the project site from San Francisco Bay and the site elevations above mean sea level would preclude risks from sea level rise, seiches, and tsunamis. Please refer to Section V.K, Greenhouse Gas Emissions and Sustainability, for a discussion of the effects of sea level rise in California and globally. Consequently, adverse impacts would be less than significant. As discussed in Section V.F, Geology, Seismicity, and Soils, the project would not result in adverse risks associated with mudflows (a type of landslide).





(5) Groundwater. The proposed project would not use groundwater for water supply. Although groundwater dewatering could be required during construction, this activity would only result in a temporary effect on the local uppermost water-bearing zones in close proximity to near-surface excavations. In the operational phase of the project, water would be provided via regional water supplies. The reduction in impervious surfaces at the project site would be expected to increase infiltration of precipitation, producing a net benefit to groundwater recharge. Therefore, adverse impacts to groundwater supplies would be less than significant.

(6) Alter the Course of a Stream or River. As noted above, the project would be expected to result in a net decrease in stormwater runoff. Runoff from the proposed project would discharge into the existing stormwater drainage system, which is adequately sized to convey runoff from the 10-year storm event. With the exception of the provision of fencing, maintenance access, and landscape/tree planting, no building/roadway construction would occur within the 50-foot buffer around Calabazas Creek, and no new bridges or utility crossings would be built over the creek. Therefore, the project would not change the course of Calabazas Creek. c. Significant Impacts. Development of the project could result in one significant impact related to hydrology and water quality, as described below. Impact HYD-1: Development of the project could result in localized flooding impacts due to inadequate storm drainage infrastructure. (S) The existing storm drain facilities within the City of Cupertino were studied in 1993 and the results were compiled in the Storm Drain Master Plan. That study determined that a portion of the existing storm drain main line located within North Wolfe Road, north of Pruneridge Avenue, does not meet current City standards. These standards require that storm drains have sufficient capacity for the 10-year storm event. As the project would widen North Wolfe Road, reroute the utilities for The Hamptons from Pruneridge Avenue to North Wolfe Road, and reconfigure utilities, including storm drains, localized storm water flows would increase, which would have adverse impacts on the under-capacity portion of the storm drain main line, and potentially other sections of the storm drain main line. (It should be noted that the substantial reduction in impervious surfaces that would result from the project would generally reduce stormwater discharges over the entire site; however, as noted above, select stormwater infrastructure may be under-sized.) Localized flooding as a result of undersized storm drainage infrastructure could potentially pose a risk to property and public safety. Implementation of the following mitigation measure would reduce this impact to a less-than-significant level:

Mitigation Measure HYD-1: As a condition of approval for construction permits, the City Engineer shall review storm drainage plans and calculations for the project, and verify whether existing storm drain infrastructure affected by the project will meet current City requirements, including the ability to convey a 10-year storm event, as storm events are calculated per standards set forth in the Santa Clara County Drainage Manual (2007). Should the City Engineer determine that the existing storm drain facilities are inadequate to convey a 10-year storm event, the project applicant shall be responsible for the design and construction of the necessary modifications. Upon completion the improvements will be dedicated to the City and the City will be responsible for ongoing maintenance, repair, and other liabilities associated with the improvements. (LTS)





d. Cumulative Impacts. Construction of the proposed project, in combination with construction of other development projects in the 14-square-mile Calabazas Creek watershed, could increase erosion and sedimentation and degrade storm water runoff quality during the construction period (i.e., when grading and excavations occur during the wet season). Implementation of existing regulatory requirements, including preparation and implementation of Stormwater Pollution Prevention Plans would be incorporated into project approvals and are required under current NPDES regulations. These measures would reduce potential construction-period cumulative impacts to a less-than-significant level. The proposed project would substantially reduce impervious surfaces on a site that currently contains little cohesive open space. The provision of additional open space on the site would result in a beneficial impact to operation-period stormwater runoff quality and quantity. In addition, the project would be required to implement operational BMPs to further improve the quality of runoff associated with operation of project. Therefore, the project would have a cumulatively beneficial impact on hydrology and water quality during the operation period (and would not make a significant contribution to adverse hydrology and water quality impacts).





This page intentionally left blank.

Date post:	13-May-2018
Category:	Documents
Upload:	lelien
View:	213 times
Download:	1 times

G. HYDROLOGY AND WATER QUALITY 1. - Amazon S3€¦ · · 2013-06-04G. HYDROLOGY AND WATER QUALITY...

Documents